Most conventional PLLs have problems with false locking onto unwanted input signals, or unwanted spectral components of the input signal. The SFPLL avoids this false locking problem as the range of frequencies to which the SFPLL can lock can be confined to an arbitrarily small region around the desired input signal (providing of course the frequency of the input signal is known with sufficient accuracy). The SFPLL typically will not false lock providing there are no unwanted input signals, or unwanted spectral components of the input signal, in the range of frequencies to which the SFPLL can lock.
Exceptionally accurate positioning and confinement of the locking range of the SFPLL can be achieved by use of precise frequency detectors and an accurate reference frequency .omega.'.sub.r.